Real secondary index theory

Abstract

In this paper, we study the family index of a family of spin manifolds. In particular, we discuss to which extend the real index (of the Dirac operator of the real spinor bundle if the fiber dimension is divisible by 8) which can be defined in this case contains extra information over the complex index (the index of its complexification). We study this question under the additional assumption that the complex index vanishes on the k-skeleton of B. In this case, using local index theory we define new analytical invariants $\hat c_k\in H^{k-1}(B;\reals/\integers)$. We then continue and describe these invariants in terms of known topological characteristic classes. Moreover, we show that it is an interesting new non-trivial invariant in many examples.